Not to bring up a zombie thread. But hy_vfd is now maintained by linuxcnc. You do not need to download the source as the module is included.
It is important to understand that some pins have been renamed or removed from what has been discussed in this thread.
It has been documented in the Linuxcnc documentation for the changes.
It took me a few days to realize that and I found a lot of information except for the above. Also I had to use a lower baud rate {9600} and for PD165 I had to use 4 to connect.
With PD165 at 3, I could not connect with parity, issue -p none
(parity none) if that happens to you using PD165 -3.